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Financial Instruments and Risk Management (Unrealized Gains (Losses) on Foreign Currency Contracts) (Details) - USD ($)
$ in Millions
 12 Months Ended
Dec. 31, 2017
Dec. 31, 2016
Disclosure of detailed information about hedged items [line items]    
Unrealized gains $ 0.3 $ (1.6)
Foreign Currency [Member]    
Disclosure of detailed information about hedged items [line items]    
Unrealized gains 13.3 2.3
Foreign Currency [Member] | Designated as Hedging Instrument [Member]    
Disclosure of detailed information about hedged items [line items]    
Unrealized gains 11.2 0.0
Foreign Currency [Member] | Not Designated as Hedging Instrument [Member]    
Disclosure of detailed information about hedged items [line items]    
Unrealized gains $ 2.1 $ 2.3